This invention relates to an improved method for preparing methylenedioxybenzene, a compound having the formula ##STR1## Methylenedioxybenzene and derivatives thereof are valuable intermediates for the preparation of compounds useful in agricultural, pharmaceutical, and veterinary fields. Methylenedioxybenzene has been especially useful in the preparation of synergists for pyrethrin insecticides. It has also been employed in the preparation of 2'-nitro-4',5'-methylenedioxyacetophenone, the starting material for the preparation of the novel antimicrobial 1-lower alkyl or alkylene substituted-6,7-methylenedioxy-4(1H)-oxocinnoline-3-carboxylic acids described in U.S. Pat. No. 3,669,965. The need for methylenedioxybenzene, augmented by the discovery of new commercial uses for the compound and its derivatives, has precipitated a search for a preparative process therefor which is more amenable to its commercial production than are the presently known processes.
Several methods have been disclosed for the preparation of methylenedioxybenzene via the reaction of catechol and a methylene dihalide under alkaline conditions. One such preparation comprises heating a mixture of catechol and a methylene dihalide in aqueous alcoholic alkali. This reaction proceeds very slowly, especially where methylene chloride is the methylenating agent, and prolonged heating under pressure is ordinarily required. An improved method for the preparation of methylenedioxybenzene from catechol and a methylene dihalide was described in U.S. Pat. No. 3,436,403 [see also W. Bonthrone and J. W. Cornforth, J. Chem. Soc. (C), 1202 (1969) and references therein] wherein it was disclosed that optimum yields for methylenedioxybenzene were obtained by carrying out the reaction in a highly polar aprotic liquid solvent medium while maintaining a high dilution of the dianions derived from the catechol. The process disclosed in U.S. Pat. No. 3,436,403 was reportedly preferably carried out by adding solid catechol and powdered alkali metal hydroxide separately, simultaneously and slowly, to a solution of methylene dichloride in a highly polar aprotic solvent. It was emphasized that the water liberated in the formation of the dianion by sodium hydroxide is an undesirable by-product, and that it is often preferable to use a base which does not produce such deleterious by-products.
A procedure, such as described in the aforementioned patent, employing simultaneous addition of two solid reactants, although easily carried out on a laboratory scale, is not so practicable on the large scale necessary for the commercial production of methylenedioxybenzene. Solutions of reagents are much more easily handled in large scale plant operations than are the solid reagents themselves. Thus a process for the preparation of methylenedioxybenzene circumventing the handling of solid reagents while still providing good yields would be advantageous.
It is an object of this invention to provide an improved method for the commercial production of methylenedioxybenzene, the improvement being realized not only in the ease of handling of the reagents but also in the yields of methylenedioxybenzene produced. It is another more specific object of this invention to provide an improved, high yielding method for the large scale preparation of methylenedioxybenzene, wherein the catechol derived dianion, in solution, is reacted with a methylene dihalide under protic alkaline conditions.